U.S. patent number 8,800,775 [Application Number 13/129,150] was granted by the patent office on 2014-08-12 for method for recovering metals from electronic waste containing plastics materials.
This patent grant is currently assigned to Terra Nova. The grantee listed for this patent is Joel Menuet, Christian Thomas, Gervais Vanhelle. Invention is credited to Joel Menuet, Christian Thomas, Gervais Vanhelle.
United States Patent |
8,800,775 |
Thomas , et al. |
August 12, 2014 |
Method for recovering metals from electronic waste containing
plastics materials
Abstract
The invention relates to a method for treating materials
containing a mixture of plastic materials and metal materials, said
method including: --crushing the material to be treated; pyrolysis
of the crushed material; a first magnetic separation performed on
the pyrolysed material providing, on the one hand, a ferrous metal
fraction and, on the other hand, non-ferrous residue; --a second
magnetic separation performed on the non-ferrous residue providing,
on the one hand, a non-ferrous metal fraction and, on the other
hand, non-magnetic residue. The invention also relates to a
facility for implementing said method.
Inventors: |
Thomas; Christian (Paris,
FR), Menuet; Joel (Billy-Montigny, FR),
Vanhelle; Gervais (Oignies, FR) |
Applicant: |
Name |
City |
State |
Country |
Type |
Thomas; Christian
Menuet; Joel
Vanhelle; Gervais |
Paris
Billy-Montigny
Oignies |
N/A
N/A
N/A |
FR
FR
FR |
|
|
Assignee: |
Terra Nova (Isbergues,
FR)
|
Family
ID: |
40790751 |
Appl.
No.: |
13/129,150 |
Filed: |
November 13, 2009 |
PCT
Filed: |
November 13, 2009 |
PCT No.: |
PCT/IB2009/055059 |
371(c)(1),(2),(4) Date: |
May 13, 2011 |
PCT
Pub. No.: |
WO2010/055489 |
PCT
Pub. Date: |
May 20, 2010 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20110220554 A1 |
Sep 15, 2011 |
|
Foreign Application Priority Data
|
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|
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Nov 14, 2008 [FR] |
|
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08 06357 |
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Current U.S.
Class: |
209/3.1; 209/214;
209/38; 209/215; 209/12.1; 209/127.1 |
Current CPC
Class: |
B07C
5/344 (20130101); B03C 1/30 (20130101); C22B
7/005 (20130101); C22B 7/001 (20130101); Y02P
10/214 (20151101); Y02P 10/20 (20151101) |
Current International
Class: |
B03D
3/00 (20060101) |
Field of
Search: |
;209/3.1,12.1,38,127.2,214,215 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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1402376 |
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Mar 2003 |
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CN |
|
0403695 |
|
Dec 1990 |
|
EP |
|
0682099 |
|
Nov 1995 |
|
EP |
|
2247287 |
|
May 1975 |
|
FR |
|
2690928 |
|
Nov 1993 |
|
FR |
|
08238472 |
|
Sep 1996 |
|
JP |
|
2001046975 |
|
Feb 2001 |
|
JP |
|
2005084839 |
|
Sep 2005 |
|
WO |
|
WO 2005084839 |
|
Sep 2005 |
|
WO |
|
Primary Examiner: Matthews; Terrell
Attorney, Agent or Firm: Nieves; Peter A. Sheehan Phinney
Bass + Green PA
Claims
The invention claimed is:
1. A method for treating materials containing a mixture of plastic
and metal materials, said method comprising: shredding the
materials to be processed; performing pyrolysis of the shredded
material; a first magnetic separation performed on the pyrolyzed
materials, providing a ferrous metal fraction and, secondly,
non-ferrous residues; a second magnetic separation performed on the
non-ferrous residues, providing, on the one hand, a non-ferrous
metal fraction and, on the other hand, non-magnetic residues
containing precious metals, and a step of combustion of the gasses
from pyrolysis, wherein the step of combustion of the gases from
pyrolysis is followed by a step of neutralizing the gas with sodium
bicarbonate.
2. The method according to claim 1, wherein the material is
electronic waste, preferably used electronic circuit boards.
3. The method according to one of claim 1 or 2, wherein the
shredding is performed down to a screen passage size D.sub.max not
exceeding 50 mm, preferably between 20 and 30 mm.
4. The method according to one of claims 1-3, wherein the pyrolysis
is performed at a temperature between 300 and 600.degree. C. and/or
with an air factor between 0.7 and 0.98.
5. The method according to one of claims 1-4, wherein the first
magnetic separation is effected by a magnet or electromagnet.
6. The method according to one of claims 1-5, wherein the second
magnetic separation is performed using an eddy current
separator.
7. The method according to one of claims 1-6, wherein the precious
metals contained in the non-magnetic residues include gold, silver,
platinum, palladium, rhodium, ruthenium, iridium and/or osmium.
8. The method according to one of claim 1-6 or 7, wherein: the
ferrous metal fraction comprises iron and/or derivatives of iron,
and possibly gold and/or the non-ferrous metal fraction comprises
aluminum and/or zinc.
9. The method according to one of claim 1-6 or 7-8, wherein the
non-magnetic residues include copper, lead, tin, glass fibers,
carbon.
10. The method according to one of claim 1-6 or 7-9, wherein the
ferrous metal fraction is combined with non-magnetic residues after
the second magnetic separation.
11. The method according to one of claim 1-6 or 7-10, comprising a
further stage of processing the non-magnetic residues to recover
the copper content in the non-magnetic residue and/or recover
precious metals contained in the non-magnetic residue in particular
selected from gold, silver, lead, tin, platinum, palladium,
rhodium, ruthenium, iridium and/or osmium.
12. A plant for treating a material containing a mixture of plastic
and metal materials, comprising successively: shredding means; a
pyrolysis facility; a flow line for collecting pyrolysis gasses
supplying a combustion chamber; at the exit from the combustion
chamber, a contact chamber fed by a supply of activated carbon and
a supply of sodium bicarbonate; a primary magnetic separator; and a
secondary magnetic separator.
13. The plant according to claim 12, wherein the shredding means
are adapted to perform shredding down to a screen passage size
D.sub.max not exceeding 50 mm, preferably between 20 and 30 mm.
14. The plant according to one of claim 12 or 13, wherein the
primary magnetic separator comprises a magnet or electromagnet
placed above a conveyor belt.
15. The plant according to one of claims 12 to 14, wherein the
secondary magnetic separator comprises a separator using eddy
currents.
Description
FIELD OF THE INVENTION
The present invention relates to a method for recovering metals
from electronic waste, notably used electronic circuit boards, and
a plant suitable for the implementation of this method.
BACKGROUND TO THE INVENTION
The increased use of computers, mobile phones, electronic equipment
and other short life high-tech devices creates a growing amount of
waste typically containing ferrous metals, copper, aluminum, zinc,
rare and precious metals. This situation poses the problem of
recovering and processing of metals contained in the waste. Thus,
such waste constitutes a veritable source of metals.
A known technique for recovery of metals is to load the waste
(previously shredded to about 4 cm) in primary ovens or copper
furnaces. This technique produces high emissions of dust, sulfur
dioxide and gases containing halogens (chlorine and bromine). The
gases thus require further complex processing. Another problem with
this technique is that electronic waste generates a lot of heat
during combustion of the plastic they contain. In other words, the
high calorific value of electronic waste is an obstacle to this
technique. The frequently high aluminum content in the treated
waste is another problem, since the presence of aluminum in the
slag or cinders increases their melting point so that treatment
becomes very difficult. Because of these various drawbacks, primary
oven capacity to handle electronic waste is limited.
Other recovery techniques use methods of fine shredding followed by
magnetic and electrostatic separation to enrich and sort phases
rich and poor in metals. For example, International application WO
2007/099204 describes a method comprising shredding the waste into
particles of 2-4 mm, electrostatic charging of the materials by
friction against a drum, followed by electron bombardment, and
finally sorting of the materials using an electric field. However,
such techniques are expensive (especially in view of the fine
shredding that is necessary), only provide imperfect sorting and
thus lead to poor performance of precious metal recovery.
In another approach, European patent EP 1,712,301 describes a
method for processing electronic waste in which metal wire
fragments are recovered from waste through a barrel provided with a
textile strip to which the wire fragments adhere.
Attempts have also been eight to recover metals by fluidized bed
pyrolysis. However, this technique has the disadvantage of mixing
the metal with an additive (fluidizing medium) such as sand, quartz
and the like, complicating recovery. Indeed, screening, which is
carried out downstream from the pyrolysis, cannot effectively
separate the additive from certain metallic dusts. Furthermore,
such a method consumes more energy, a part of the metals gets
oxidized and metals are entrained in the gas phase.
There is therefore a real need to develop a method for recovering
the metals contained in electronic waste, which overcomes the
disadvantages mentioned above. In particular, it is desirable to
develop a simple the that consumes relatively little energy, does
not require extensive treatment of the gases emitted, and makes it
possible to obtain a good yield of recycled metals.
SUMMARY OF THE INVENTION
The invention firstly provides a method for treating materials
containing a mixture of plastic and metal materials, said method
comprising: shredding the materials to be processed; pyrolysis of
the shredded material; a first magnetic separation performed on the
pyrolyzed materials, providing a ferrous metal fraction and,
secondly, non-ferrous residues; a second magnetic separation
performed on the non-ferrous residues, providing, on the one hand,
a non-ferrous metal fraction and, on the other hand, non-magnetic
residues containing precious metals.
According to one embodiment, the material is electronic waste,
preferably used electronic circuit boards.
According to one embodiment, the shredding is performed down to a
screen passage size Dmax not exceeding 50 mm, preferably between 20
and 30 mm.
According to one embodiment, the pyrolysis is performed at a
temperature between 300 and 600.degree. C. and/or with an air
factor between 0.7 and 0.98.
According to one embodiment, the first magnetic separation is
effected by a magnet or electromagnet.
According to one embodiment, the second magnetic separation is
performed using an eddy current separator.
According to one embodiment, the method further comprises a step of
combustion of the gases from pyrolysis, optionally followed by a
step of neutralizing the gas with sodium bicarbonate.
The precious metals can include gold, silver, platinum, palladium,
rhodium, ruthenium, iridium and/or osmium.
According to one embodiment: the ferrous metal fraction comprises
iron and/or derivatives of iron, and possibly gold and/or the
non-ferrous metal fraction comprises aluminum and/or zinc.
The non-magnetic residues can include copper, lead, tin, glass
fibers, carbon.
According to one embodiment of the method, the ferrous metal
fraction is combined with non-magnetic residues after the second
magnetic separation.
According to one embodiment, the method comprises a further stage
of processing the non-magnetic residues to recover the copper
content in the non-magnetic residue and/or recover precious metals
contained in the non-magnetic residue in particular selected from
gold, silver, lead, tin, platinum, palladium, rhodium, ruthenium,
iridium and/or osmium.
The invention also provides a plant for treating material
containing a mixture of plastic and metal materials, comprising
successively: shredding means; a pyrolysis facility; a primary
magnetic separator, and a secondary magnetic separator.
According to one embodiment, the shredding means are adapted to
perform shredding down to a screen passage size Dmax not exceeding
50 mm, preferably between 20 and 30 mm.
According to one embodiment of the plant, the primary magnetic
separator comprises a magnet or electromagnet placed above a
conveyor belt.
According to one embodiment of the plant, the secondary magnetic
separator comprises a separator using eddy currents.
According to one embodiment of the plant, it further comprises a
line for collecting pyrolysis gases supplying a combustion chamber,
and optionally, at the exit from the combustion chamber, a contact
chamber fed by a supply of activated carbon and a supply of sodium
bicarbonate.
The present invention overcomes the disadvantages of the prior art.
It specifically provides a simple and energy-efficient process,
giving a good yield of recycled metals.
This is accomplished through the surprising finding that the direct
pyrolysis of materials that have previously been coarsely ground or
shredded (fine shredding being unnecessary) makes it possible to
directly obtain a mixture of the various constituents in a
separated form: notably carbon-containing residues on the one hand
and the various other metals on the other hand.
According to certain particular embodiments, the invention also has
one or more of the advantageous features listed below. The method
of the invention makes it possible to eliminate epoxy resins and
plastic components of electronic circuit boards as well as chlorine
and a major portion of bromine while avoiding metal loss by
oxidation or distillation in view of the low temperature and
non-oxidizing conditions of the operation. The material is thus
concentrated in metals. The method of the invention makes it
possible, during the cooling of combustion gases from gases
produced during pyrolysis, to recover, under favorable conditions,
the energy contained in these gases. The material thus pyrolyzed
can advantageously be treated in conventional tools of copper
metallurgy thereby overcoming certain technological limitations of
these tools and more specifically volatile matter content (carbon
chains) and halogens. In the case of electronic card processing,
the decomposition of epoxy resins during pyrolysis has the effect
of freeing all the components rendered integral with the base
material: copper, electronic components, metal components, and so
on. This separation from the base material allows a very efficient
use of magnetic sorting (being more effective than separation
performed by shredding very finely). The method of the invention
maximizes the efficiency of metal recovery, other words minimizes
losses of metal during the process. The method of the invention
makes it possible to separate aluminum from other metals during the
process, so as to facilitate downstream processing of the metals
recovered. In the case of pyro-metallurgical processes, aluminum
does indeed have a behavior detrimental to the fluidity of slag. In
the case of hydrometallurgical processes, aluminum because of its
chemical reactivity leads to overconsumption of chemicals.
Treatment of gases from the pyrolysis (including post-combustion)
makes it possible to render the method clean without requiring any
heavy manipulation of halogens, sulfur compounds or heavy metal
emissions.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows schematically an example of plant for electronic waste
processing according to the invention.
DESCRIPTION OF EMBODIMENTS OF THE INVENTION
The invention will now be described in more detail and in a
non-limiting fashion in the following description.
Plant for Treating for Electronic Waste
Referring to FIG. 1, a plant for treating for electronic waste
according to the invention comprises the following elements, shown
schematically.
Input of the plant for treating is provided by a supply line for
electronic waste in bulk 1. This supply line 1 for electronic waste
supplies shredding and sampling means 2. The shredding and sampling
means may include a primary crusher to reduce the size of the waste
to less than 50 mm, a primary sampler to collect a primary sample
representative of total inflow (e.g. 10% of total inflow) a second
mill to grind the primary sample to a size of 10 mm, a secondary
sampler representative of the primary sample (e.g. 10% of the flow
of the primary sample), optionally a third crusher and a tertiary
sampler.
A preferred example of the primary crusher is a knife mill equipped
with a 25 mm grid. This type of grinder has the advantage of
limiting the production of fines.
At the exit from the shredding and sampling means 2, a shredded
waste supply line 3 supplies shredded waste to a pyrolysis facility
4. A buffer silo (not shown) may be provided between the shredding
and sampling means 2 and the pyrolysis facility 4. The pyrolysis
facility 4 may in particular be a screw conveyor furnace, a
reverberatory furnace, a rotary furnace, a fluidized bed furnace, a
multistage furnace and the like.
Preferably, the pyrolysis facility is a multistage furnace, for
example of about 100 m.sup.2, directly gas heated. The facility can
typically have a power of around 1000 kW.
At the exit from the pyrolysis facility 4, there are provided a
flow line 5 for conveying pyrolyzed residues and a conduit for
collecting pyrolysis gases 15.
The flow line 5 for conveying pyrolyzed residues supplies cooling
means 6. The cooling means 6 can notably include a heat exchanger.
A jacketed screw of about 50 m.sup.2 surface area and cooled by
water may be particularly suitable.
At the outlet of cooling means 6, a supply line 7 for cooled
residues feeds a primary magnetic separator 8. The primary magnetic
separator 8 may be a simple electromagnet placed above a conveyor
belt.
A recovery line for the ferrous metal fraction 9 and a recovery
line for non-ferrous residues 10 are connected at the exit from
primary magnetic separator 8.
The recovery line for non-ferrous residues 10 in turn feeds a
secondary magnetic separator 11, specially designed for this
function. The secondary magnetic separator 11 can for example make
use of eddy currents.
A recovery line for the non-ferrous metal fraction 12 and a
recovery line for non-magnetic residues 13 are connected at the
exit from the secondary magnetic separator 11. The recovery line
for non-magnetic residues 13 in turn feeds conditioning means
14.
In one particular embodiment, the conduit for collecting pyrolysis
gas 15 feeds a combustion chamber 17, which is also supplied by an
air inlet pipe 16. The combustion chamber 17 may be of a
cylindrical metal chamber type protected by one or more layers of
bricks.
At the exit from the combustion chamber 17, a combustion products
collection line 18 feeds cooling means 19. The cooling means 19 may
for example consist of a cooling tower 19, operating by injection
of a water spray 20, or a flue gas heat exchanger (air/flue gas or
water-flue gas) and cooler.
A flow line for collecting cooled combustion products 26 is
connected to the outlet of the cooling means 19 and supplies a
contact chamber 29. An addition of activated carbon 27 and an
addition of sodium bicarbonate 28 are also provided at the inlet to
the contact chamber 29. The contact chamber 29 can be of the
cylindrical type having sufficient volume to provide a residence
time of combustion products of about two seconds.
At the outlet from the contact chamber 29, a collection line for
treated products 30 feeds a filter 31 at the outlet from which
there are provided a recovery line 33 for purified gas and a flow
line for halogen recovery 32. The filter 31 may be of the bag
filter or electro-filter type.
In one possible embodiment, a preliminary cooling system can be
provided upstream of the cooling means 19. This cooling system
includes a preliminary sampling line 21 at the outlet from
combustor chamber 17 which feeds a heat exchanger 24, then joining
the line for collecting combustion products 18. The heat exchanger
24 is also fed by a supply of heat transfer flue 23. Exit 25 of the
heat transfer fluid provides for energy recovery.
Method of Processing Electronic Waste
We describe below an example of a method for processing electronic
waste making it possible to put the metals they contain to further
use.
By "electronic waste" we mean used materials that include
electronic components. Electronic waste may include individual
electronic components, mobile phones and other small devices
containing circuit boards. Preferably, the electronic waste
comprises or consists of electronic circuit boards, that is to say,
consists of printed circuit boards on which electronic components
are soldered. The remainder of the process is described in
connection with the recycling of electronic circuit boards.
The method is however also applicable to the case of other types of
starting materials, i.e. in general materials (preferably used
materials or waste) that include a certain percentage or metal
(notably including a fraction of metal containing precious metals)
and a plastic fraction. The plastic fraction may include notably
epoxy resins, polyethylene or polyvinyl chloride. The metal
fraction for its part may include, notably, ferrous metals, copper,
lead, aluminum, zinc, precious metals (gold, silver, platinum,
palladium, rhodium, ruthenium, iridium, osmium). For example, the
method can be applied to automotive shredder residue.
The method described here includes five main steps:
(1) shredding;
(2) pyrolysis;
(3) cooling;
(4) magnetic sorting, and
(5) gas treatment.
This example corresponds to the operation of the plant for treating
described above in connection with FIG. 1.
The treatment capacity is of about 3 tons per hour.
In step (1), electronic circuit boards are crushed in the shredding
means 2. Shredding is preferably done down to a size Dmax of 25 mm
(Dmax is defined as the screen passage size). The shredded up
circuit boards are then stored in a buffer silo.
The buffer silo feeds at a rate of about 3 tons per hour the
pyrolysis facility 4, wherein the pyrolysis is performed at step
(2). For this step (2), the shredded up circuit boards are heated
up in the furnace to a temperature of between 300 and 450.degree.
C., preferably about 400.degree. C. in a suitable reactor,
essentially in the absence of oxygen (under reducing or neutral
conditions). More specifically, the burners are adjusted to be poor
in air and the air factor (ratio between combustion air and the
theoretical air for neutral combustion) is between 0.7 and 0.9. The
duration of pyrolysis is adjusted to obtain complete decomposition
of the carbon chains that make up the plastic fraction (notably the
epoxy resin chains). For example, the duration can be between 10
and 30 minutes. An addition of about 1 ton of steam per hour at the
floor of the multistage furnace makes it possible to control the
temperature thereof.
During step (3), pyrolysed residues pass through the cooling means
6. This step makes it possible to reduce the temperature of the
pyrolysed residues down to a temperature of between 60 and
100.degree. C.
Then, step (4) includes the actual separation of metals. This step
makes it possible to enrich the solid residues in precious metals
and to reduce the concentration in components harmful to the
subsequent treatment of the pyrolyzed residues (notably
aluminum).
In a first step, the cooled residues passes through the primary
magnetic separator 8, typically a simple electromagnet placed above
a conveyor belt. Thereby, extraction of the ferrous metal fraction
residues is achieved. This ferrous metal fraction comprises mainly
iron and iron compounds, but eventually, depending on the origin of
the electronic circuit boards, the ferrous metal fraction may also
include (be mixed with) gold. This is particularly the case when
electronic circuit boards are gold flashed. Preferably, the ferrous
metal fraction comprises not more than 1% aluminum.
In a second step, the residues free of their ferrous metal fraction
undergo a magnetic extraction of non-ferrous, at a secondary
magnetic separator 11, typically using eddy currents. Thus, a
non-ferrous metal fraction, which includes notably aluminum and
zinc is extracted. The aluminum can be recovered and sold for
recycling. On the other hand, the remaining residues (nonmagnetic
residues) are recovered via the recovery line for non-magnetic
residues 13. Preferably, the non-magnetic residues does not
comprise more than 2% aluminum.
To perform the magnetic extraction of non-ferrous using eddy
currents, it is important that the non-ferrous metal fraction
(including aluminum) be essentially in non-oxidized form.
Therefore, the method is implemented so that the metals making up
the non-ferrous metal fraction, and primarily aluminum, are not
oxidized before the magnetic extraction step for non-ferrous
metals. Typically, when heated by direct flame, flame adjustment is
set to be deficient in oxygen (typically 90% of the stoichiometric
amount); in case of indirect heating, the atmosphere must be
reducing. Furthermore, it is preferable to work below the melting
point of aluminum, to avoid traces of oxygen oxidizing the molten
metal (easier to oxidize than solid metal).
Depending on the precious metal content of the ferrous metal
fraction, it is possible either to separately prepare the fraction
of metallic iron for further use or to once again makes it with the
residual non-magnetic fraction after the second magnetic separation
(at the recovery line for non-magnetic residues 13).
Preparing the ferrous metal fraction for reuse may include recovery
of precious metals it contains, for example by the following
methods: recycling the magnetic part rich in precious metals at the
input to the copper furnaces, and processing of anode slimes from
electro-refining of copper anodes running out at the exit from the
furnace; washing the magnetic portion with a wash including lead in
order to solubilize the precious metals in the lead, and processing
the lead by any conventional method for recovering the precious
metals (such as zinc plating, distillation and cupellation, or
treatment of a Betts electrorefining type).
Non-magnetic residues include notably carbon, glass fibers, copper,
lead, tin and precious metals generally. The precious metals in
question may include gold, silver, platinum, palladium, rhodium,
ruthenium, iridium and/or osmium. These non-magnetic residues are
then packed in so-called big bags or in bulk to be treated either
by hydrometallurgical or pyrometallurgical processes.
Hydrometallurgy may include a step of attack by sulfuric acid in an
oxidizing environment, followed by electrowinning to recover the
copper, the residues of attack being reduced in a rotary furnace
containing lead in order to solubilize the precious metals, the tin
and the lead. The lead and tin can be refined by Betts type
electrolysis, the sludge containing essentially precious
metals.
Regarding the pyrometallurgical treatment, the residues are
recycled to the entry to the copper furnaces, after which the anode
sludge from the electro-refining of copper anodes running at the
furnace exit are treated.
As for step (5), it can be performed concurrently with step (2),
since it concerns the treatment of gases produced by pyrolysis.
Gases from pyrolysis contain combustion products from burners,
water vapor and gases from the decomposition of epoxy resins and
other carbon chain materials.
These gases are burned in the combustion chamber 17 to a
temperature sufficient to allow the destruction of dioxins. A
temperature between about 850 and about 1100.degree. C. may be
appropriate. Hydrochloric acid and hydrobromic acid are thus
produced.
After cooling the gas to a temperature between about 180 and about
200.degree. C. (at cooling means 19), an injection of activated
carbon (e.g., about 50 mg/m.sup.3) and sodium bicarbonate
(typically about 20 kg/h) is performed in order to fix the
remainder of the dioxins and to cause the HCl and HBr to react with
the sodium bicarbonate to form sodium bromide and sodium chloride.
The reactions take place in the contact chamber 29, with a contact
time of about 2 seconds.
After filtration, essentially a mixture of sodium bromide and
sodium chloride is recovered, the mixture can be further processed
for recovery of bromine.
It is also possible to arrange to extract energy from the
combustion products (heat exchange at heat exchanger 24), this
energy being then able to be recycled to other steps of the
process.
Note that step (5) can be advantageously replaced by a step of
condensation of the gas phase for recovery and recycling of
products from the decomposition of carbon chains (phenol,
bisphenol, bromophenol and other components).
EXAMPLE
This example below illustrates the invention without limiting
it.
It implements the method described above for treating used
electronic circuit boards. It reintroduces the ferrous metal
fraction after the second magnetic separation. The table below
provides an estimate of changes in the chemical composition of the
products at different stages of the process.
TABLE-US-00001 Raw After After double waste pyrolysis magnetic
separation Cu (%) 17 23 24.5 Al (%) 6.5 8.8 2.8 Fe (%) 5 6.7 7.14
Precious 1000 1350 1440 metals (g/t) Carbon chains (%) 34 0 0
Carbon (%) 0 11.1 11.8 Cl (%) 0.4 0.0 0.0 Br (%) 0.6 0.3 0.0
SiO.sub.2 (%) 22 29.7 31.6
* * * * *